Field of the Invention
Embodiments of the present invention relate to an organic light emitting device and, more particularly, to an organic light emitting device capable of simplifying a manufacturing process, enhancing efficiency and reducing power consumption, and a method of fabricating the same.
Description of the Related Art
An organic light emitting diode (OLED) display is a self-luminous display employing an organic light emitting device. The organic light emitting device has an emission layer between an a cathode serving as an electron injection electrode and an anode serving as a hole injection electrode. The organic light emitting device receives electrons from the cathode and holes from the anode and injects the electrons and the holes into the emission layer. The injected electrons are combined with the injected holes to form excitons. The organic light emitting device emits light when the excitons transit from an excited state to a ground state.
OLED displays are classified into a top emission type, a bottom emission type, and a dual emission type according to emission directions of light from the OLEDs, and are also classified into a passive matrix type and an active matrix type according to manners in which the OLEDs are driven.
Contrary to the liquid crystal display (LCD), the OLED display requires no separate light source. Accordingly, a lightweight and thin OLED display can be fabricated. The OLED display is advantageous in terms of power consumption since the OLED display requires a low driving voltage. Moreover, the OLED display exhibits excellence in color expressions, response time, viewing angle and contrast ratio (CR). For these reasons, the OLED display is under research as a next generation display.
With development towards higher-definition displays, the number of pixels per unit area has increased, and higher brightness has been demanded. However, the OLED display has a limit on current (A) per unit area due to the emission structure of the OLED display. In addition, increasing the current applied to the organic light emitting device leads to lower reliability and increased power consumption of the organic light emitting device.
FIG. 1 is a view schematically illustrating the structure of an organic light emitting device 100 of the related art.
Referring to FIG. 1, the organic light emitting device 100 of the related art includes a first electrode 110 (anode) formed on a substrate on which a red sub-pixel area Rp, a green sub-pixel area Gp and a blue sub-pixel area Bp are defined, a hole injection layer (HIL) 115, a common hole transporting layer (common HTL) 120, a first hole transporting layer 125 (R-HTL), a second hole transporting layer 130 (G-HTL), organic emission layers including a red emission layer (red EML) 135, a green emission layer (green EML) 140 and a blue emission layer (blue EML) 145, an electron transporting layer (ETL) 150, a second electrode 155 (cathode), and a capping layer (CPL) 160.
As shown in FIG. 1, for the organic light emitting device 100, the red EML 135, the green EML 140 and the blue EML 145 are patterned on the red sub-pixel area Rp, the green sub-pixel area Gp and the blue sub-pixel area Bp respectively using a fine metal mask (FMM). As the organic emission layers are formed using the FMM as above, the fabrication process of the organic light emitting device becomes complex and productivity of the organic light emitting device is lowered.
In addition, emission efficiency of the organic light emitting device 100 may be improved by adjusting thicknesses of the first and second hole transporting layer 125 and 130 and the organic emission layers 135, 140 and 145 in the respective sub-pixel areas to produce a micro cavity effect. However, since a structure having a second-order optical distance is applied to all of the red sub-pixel area Rp, the green sub-pixel area Gp and the blue sub-pixel area Bp, the red EML 135 in the red sub-pixel area Rp becomes thicker than the green EML 140 in the green sub-pixel area Gp and the blue EML 145 in the blue sub-pixel area Bp.
Due to the thickness of the red EML 135 of the red sub-pixel area Rp formed as above, the driving voltage of the organic light emitting device 100 significantly increases along with an increase in power consumption.
Further, as the red EML 135 becomes relatively thick, an opening of a mask is clogged by organic material in the deposition process of the thick organic emission layer. This phenomenon is called mask rib. The mask rib leads to a poor organic light emitting device.
Accordingly, it is needed to overcome technological limitations on emission efficiency, lifetime and power consumption that deteriorate the quality and productivity of the OLED display. Currently, research is being widely conducted to develop an organic light emitting device which is capable of enhancing emission efficiency, lifetime of the organic emission layer and viewing angle while maintaining the color gamut.